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These squirrel-size monkeys helped bring Peru’s Amazon back to life

The lush Amazon rainforest of northeastern Peru lost most of its trees when it was logged and converted to pastures for water buffalo in 1990. But after humans abandoned the area about 10 years later, the forest slowly began to regrow. Now, scientists have an explanation for how it revived so quickly: the foraging activities of tamarins, squirrel-size monkeys native to the area.

Scientists long suspected the tamarins had played a role. So, for more than 20 years, researchers used GPS tracking devices and field observations to measure how much time the monkeys spent in the previously logged forest. The researchers also tracked how often and where the monkeys excreted seeds they ate from fruit trees—most of which came from a nearby forest.

During the first 3 years, the monkeys spent less than 1.5% of their time in the previously logged forest, but by 2016, this increased to about 12%. Of the hundreds of seeds researchers tracked, 15 survived and grew into trees that were taller than 2 meters. Researchers collected their leaves and analyzed their genes; more than half of the trees sprouted from seeds that originally came from the nearby forest. This confirms that the monkeys play a critical role in bringing deforested areas back to life, the researchers report today in Scientific Reports.

Although the forest has been recovering for more than 20 years, it still does not have the plant diversity and coverage that would provide the monkeys with a suitable home. For that, only time will tell how long it might take for the forest to make a full comeback.